Ammonium Persulfate Concentration Research Articles

Synthesis, characterization, and swelling behavior of alginate‐g‐poly(sodium acrylate)/kaolin superabsorbent hydrogel composites

AbstractA novel superabsorbent composite based on sodium alginate and the inorganic clay kaolin was synthesized via the graft copolymerization of acrylic acid (AA) in an aqueous medium with methylene bisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The effects of reaction variables, such as the MBA, AA, and APS concentrations and the alginate/kaolin weight ratio, on the water absorbency of the composite were systematically optimized. Evidence of grafting and kaolin interactions was obtained by a comparison of the Fourier transform infrared spectra of the initial substrates with that of the superabsorbent composite, and the hydrogel structure was confirmed with scanning electron microscopy. The results indicated that with an increasing alginate/kaolin weight ratio, the swelling capacity and gel content increased. The effects of various salt media were also studied, along with the swelling kinetics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Preparation of Nanometre Carbon Fibres by Using a Blend Approach

PMMA/PAN core/shell microspheres were synthesised by polymerising methyl methacrylate (MMA) or acrylonitrile(AN) at 75 °C for 5 h in a soapless emulsion system, using ammonium persulfate (APS) as a radical initiator. It has been shown that in the first-stage reaction the initiator APS significantly accelerated the reaction rate. However, when the APS concentration reached 0.9% (based on the amount of the monomers), this tendency lessened. In the second-stage core/shell reaction, the effect of initiator on reaction rate was not so pronounced. Transmission electron microscope (TEM), fourier transform infrared (FT-IR), thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were used to characterise the structure and properties of seeded PMMA core and/or PMMA/PAN core/shell polymers. The core/shell morphology was clearly displayed and the diameter of the core is ca. 350 nm whereas the shell thickness was ca. 100 nm. Both the PMMA core and the PMMA/PAN core/ shell polymers had weak and strong endothermic peaks when heated in the range of 340–390 °C, but the latter showed a characteristic exothermic peak which corresponded with the crosslinking reaction of polyacrylonitrile macromolecules at ca. 600 °C. A mixture was obtained by blending the core/shell polymers with high density polyethylene, then spinning to form composite fibres, which were thermally stabilised in air at 180 °C for 1 h and carbonised in nitrogen at 1000 °C to obtain nanometre-sized carbon fibres.

Feasibility Study of an Aqueous Zinc−Persulfate Battery

In a zinc−persulfate battery, active metal-zinc pieces were used as an anode and ammonium chloride as an electrolyte in an anode zone, with soluble oxidants−persulfate as an active cathode substance and electrolyte in the cathode zone. Carbon felt was used as an inert cathode, with a PE-01 homogeneous membrane between the anode and cathode zones as well as 100 mL of solution in both the anode and cathode zones. The discharge characteristics of the battery at 5 Ω was investigated for various temperatures and concentrations of ammonium persulfate, sodium persulfate, and ammonium chloride, and a flat discharge characteristic was obtained. The output energy of the zinc−persulfate battery increases remarkably on increasing the concentrations of persulfate and ammonium chloride, as well as temperature. The output energy of the zinc−sodium persulfate battery is greater than that of a zinc−ammonium persulfate battery. If the concentration of ammonium persulfate is less than or equal to 1.25 M, crystals did not form in the cathode zone after discharge when the temperature was above 0 °C. Crystals formed are a mixture of (NH4)2Zn(SO4)2·6H2O, (NH4)2Zn(SO4)2, (NH4)2SO4, and (NH4)3H(SO4)2. (NH4)2Zn(SO4)2 is the major constituent, and the others are the minor ones. The maximal and least actual gravimetric energy densities of the Zn−(NH4)2S2O8 battery are 48.15 and 20.78 W h kg-1, respectively.

Facile synthesis of poly(hydroxyethyl acrylate) by frontal free‐radical polymerization

AbstractWe report the first synthesis of poly(hydroxyethyl acrylate) (PHEA) without solvent by free‐radical frontal polymerization (FP) at ambient pressure. In a typical run, the appropriate amounts of reactant (hydroxyethyl acrylate) and initiator (1,1‐di(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane) (Luperox 231) were mixed together at ambient pressure. FP was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self‐propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. To study the macrokinetics, we also produced PHEA frontally with ammonium persulfate as initiator and dimethyl sulfoxide as the solvent. The dependences of the front velocity and front temperature on the initiator concentration and reactant dilution were investigated. The front temperatures were between 124 and 157 °C, depending on the ammonium persulfate concentration. Thermogravimetric analysis indicates that PHEA prepared by FP with ammonium persulfate as initiator had higher thermal stability than solvent‐free frontally prepared PHEA with Luperox 231 as initiator. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 873–881, 2007

Carrageenan-g-Poly(sodium Acrylate)/Kaolin Superabsorbent Hydrogel Composites: Synthesis, Characterisation and Swelling Behaviour

A novel superabsorbent hydrogel composite based on kappa-carrageenan (κC) was prepared by graft copolymerisation of acrylic acid (AA) in the presence of kaolin using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The synthetic variables (i.e. AA, MBA and APS concentration, and the amount of kaolin) affecting the water absorbency of the resulting superabsorbent composite were studied. Evidence of grafting and kaolin interaction was obtained by comparing the FTIR spectra of the initial substrates and of the superabsorbent composite. A new absorption band at 1722 cm−1 in the composite spectrum confirmed the kaolin-organic polymer linkage. Increasing the amount of kaolin and the MBA concentration caused the water absorbency of the superabsorbent composite to decrease. The effect of various salt media and pH on the swelling of the superabsorbent was studied. The swelling kinetics of the synthesised composite was also investigated.

Synthesis and absorbency of gelatin-graft-poly(sodium acrylate-co-acrylamide) superabsorbent hydrogel with saltand pH-responsiveness properties

AbstractIn this article, we synthesize a novel gelatin-based superabsorbent hydrogel via graft copolymerization of mixtures of acrylic acid (AA) and acrylamide (AAm) onto gelatin backbones. The polymerization reaction was carried out in an aqueous medium and in the presence of ammonium persulfate (APS) as an initiator and N,N'-methylene bisacrylamide (MBA) as a crosslinker. The hydrogel structures were confirmed by FTIR spectroscopy. The effect of grafting variables, i.e. concentration of MBA and APS, AA/AAm weight ratio, and reaction time and temperature, was systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The swelling behavior of these absorbent polymers was also investigated in various salt solutions. Results indicated that the swelling capacity decreased with an increase in the ionic strength of the swelling medium. Furthermore, the swelling of superabsorbing hydrogels was examined in solutions with pH values ranging between 1.0 and 13.0. It showed a reversible pH-responsive behavior at pHs 2.0 and 7.0. This on-off switching behavior makes the synthesized hydrogels an excellent candidate for controlled delivery of bioactive agents. Finally, the swelling kinetics of the synthesized hydrogels with various particle sizes was preliminarily investigated.

CMC-g-Poly (Sodium Acrylate)/Kaolin Superabsorbent Hydrogel Composites: Synthesis, Characterization and Swelling Behaviour

A novel superabsorbent composite system based on carboxymethyl cellulose (CMC) was prepared by graft copolymerization of acrylic acid (AA) in the presence of kaolin powder using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The effect of reaction variables, such as MBA, AA, and APS concentration and CMC/kaolin ratio on the water absorbency of the composite were studied. Evidence of grafting and kaolin interaction was obtained by comparing the FT-IR spectra of the initial substrates with that of the superabsorbent composite. The results indicated that with increasing amount of kaolin, the swelling capacity was increased and then considerably decreased with further increase in amount. The effect of various salt media was also studied, along with swelling kinetics.

MBA-crosslinked Na-Alg/CMC as a smart full-polysaccharide superabsorbent hydrogels

A novel superabsorbent hydrogel composed of carboxymethylcellulose (CMC) and sodium alginate (Na-Alg) was prepared by using methylenebisacrylamide (MBA) as a crosslinking agent. Ammonium persulfate (APS) was used as an initiator. For investigation of the effect of reaction variables on water absorbency of the hydrogels, the synthetic conditions were systematically optimized through studying the influential factors, including temperature, Na-Alg/CMC weight ratio and concentration of MBA and APS. Increase in MBA and APS concentration results in the decrease in water absorbency of the hydrogels. The water absorbency of the hydrogels increased with increasing of reaction temperature and Na-Alg/CMC weight ratio up to 85 °C and 0.54, respectively. The hydrogel was identified using FT-IR spectroscopy and SEM pattern. These behaviors were discussed according to structural parameters. The influence of variables such as pH, particle size and MBA concentration on the swelling kinetics of the hydrogels was investigated. The water absorbency of these hydrogels in various salt solutions was studied. The tendency of the absorbency for these hydrogels in salt solutions is in the order Na + > Ca 2+ > Al 3+ for NaCl, CaCl 2 and AlCl 3 aqueous salt solutions. The results showed that the water absorbency for the hydrogels in monovalent cations salt solutions is in order LiCl > NaCl > KCl. Crosslinked Na-Alg/CMC hydrogels exhibited a reasonable sensitivity to the pH.

Synthesis, Characterization, and Application of Poly(Acrylamide)/Poly(Vinyl Alcohol) Polyblends

ABSTRACT Free radical polymerization of acrylamide (Aam) in the presence of aqueous solution of three commercial grades of polyvinyl alcohol (PVOH), namely, Vinarol FV (containing very few acetyl groups), Mowiol 4-80 (low viscosity-partially hydrolyzed), and Vinarol STH (medium viscosity-partially hydrolyzed), using ammonium persulfate (AP) initiator resulted in three corresponding PVOH/Aam polyblends. Optimum polymerization conditions were PVOH and AP concentrations, 10% and 0.05 mol/L, respectively; Aam concentration, 50% based on the weight of PVOH; polymerization temperature and time, 70°C and 20 min, respectively; rate of stirring, 200 rpm, at which the three polyblends were prepared at very high polymerization extent ranging from 98.2 to 99.9%. Rheological properties of 10% aqueous solutions of the polyblends at 80°C were studied. The extent of film resolubility of PVOH's and their polyblends follows the descending order: Mowiol®4-80/Aam > Mowiol®4-80 > Vinarol®STH/Aam > Vinarol®STH > Vinarol®FV/Aam > Vinarol®FV. Sizing of gauzy cotton fabric with the polyblends and PVOH's showed that (1) their tensile strength follows the order: Vinarol®STH/Aam > Vinarol®STH > Mowiol®4-80/Aam > Mowiol®4-80 > Vinarol®FV/Aam > Vinarol®FV > Unsized and (2) their desizability follows the order: Mowiol®4-80/Aam > Mowiol®4-80 > Vinarol®STH/Aam > Vinarol®STH > Vinarol®FV/Aam > Vinarol®FV.

Preparation of a Chemical Polyblend Sizing Agent via Polymerization of Acrylic Acid with Polyvinyl Alcohol

ABSTRACT A polyblend sizing agent was prepared by free radical polymerization of partially neutralized acrylic acid (AA) in the presence of polyvinyl alcohol, (PVOH) (Vinarol®DV of Clariant), using ammonium persulfate (AP) initiator. Polymerization was conducted under different conditions including AP concentration (0.025–0.125 mol/L), degree of neutralization (3–50%), time (0–60 min), temperature (50–80°C), AA/PVOH ratio (0.2:1.2), type of neutralizing agent (NaOH or NH4OH), and PVOH concentration (50–150 g/L). At optimum polymerization conditions, 100 g/L PVOH, 75 g/L AA (3% neutralized using NH4OH), 0.1 mol/L AP, at 70°C for 25 min, a polyblend was prepared with a percent total conversion of 94%. It was then neutralized with NaOH to a pH of 7. Rheological properties of 10% aqueous solution of the polyblend or PVOH at 80°C revealed that the first was of a non-Newtonian pseudoplastic flow and the latter is of a non-Newtonian thixotropic flow. Solubility time of the polyblend film was shorter than that of PVOH, either after thermal treatment (120°C/15 min)or without thermal treatment. Sized gauzy fabric samples using the polyblend were of higher tensile strength and extent of size removal than those sized with PVOH.

Chitosan-g-Poly(Acrylic Acid)/Kaolin Superabsorbent Composite: Synthesis and Characterization

A novel superabsorbent composite based on chitosan was prepared by graft copolymerization of acrylic acid (AA) in the presence of kaolin powder using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The synthetic variables (i.e. AA, MBA, and APS concentration, and the kaolin amount) affecting the water absorbency of the resulting superabsorbent composite were studied. Evidence of grafting and kaolin interaction was obtained by comparing the FTIR spectra of the initial substrates with that of the superabsorbent composite. A new absorption band at 1722 cm−1 in the composite spectrum confirmed the kaolin-organic polymer linkage. The effect of kaolin amount showed that increasing this parameter caused the water absorbency of the superabsorbent composite to decrease. The effect of pH on the water absorbency of the superabsorbent was also studied.

RAFT-Mediated Emulsion Polymerization of Styrene using a Non-Ionic Surfactant

We report the successful RAFT-mediated emulsion polymerization of styrene using a non-ionic surfactant (Brij98), the highly reactive 1-phenylethyl phenyldithioacetate (PEPDTA) RAFT agent, and water-soluble initiator ammonium persulfate (APS). The molar ratio of RAFT agent to APS was identical in all experiments. Most of the monomer was contained within the micelles, analogous to microemulsion or miniemulsion systems but without the need of shear, sonication, cosurfactant, or a hydrophobe. The number-average molecular weight increased with conversion and the polydispersity index was below 1.2. This ideal ‘living’ behavior was only found when molecular weights of 9000 and below were targeted. It was postulated that the rapid transportation of RAFT agent from the monomer swollen micelles to the growing particles was fast on the polymerization timescale, and most if not all the RAFT agent is consumed within the first 10% conversion. In addition, it was postulated that the high nucleation rate from the high rate of exit (of the R radical from the RAFT agent) and high entry rate from water-phase radicals (high APS concentration) reduced the effects of ‘superswelling’ and therefore a similar molar ratio of RAFT agent to monomer was maintained in all growing particles. The high polydispersity indexes found when targeting molecular weights greater than 9000 were postulated to be due to the lower nucleation rate from the lower weight fractions of both APS and RAFT agent. In these cases, ‘superswelling’ played a dominant role leading to a heterogeneous distribution of RAFT to monomer ratios among the particles nucleated at different times.

Modified carrageenan. 6. crosslinked graft copolymer of methacrylic acid and kappa-carrageenan as a novel superabsorbent hydrogel with low salt- and high pH-sensitivity

A novel, polysaccharide-based, superabsorbent hydrogel was synthesized through crosslinking graft copolymerization of methacrylic acid (MAA) onto kappa-carrageenan (κC), using ammonium persulfate (APS) as a free radical initiator in the presence of methylenebisacrylamide (MBA) as a crosslinker. A proposed mechanism for κC-g-polymethacrylic acid (κC-g-PMAA) formation was suggested and the hydrogel structure was confirmed using FTIR spectroscopy. The effect of grafting variables, including MBA, MAA, and APS concentration, was systematically optimized to achieve a hydrogel with the maximum possible swelling capacity. The swelling kinetics in distilled water and various salt solutions were preliminarily investigated. Absorbency in aqueous salt solutions of lithium chloride, sodium chloride, potassium chloride, calcium chloride, and aluminum chloride indicated that the swelling capacity decreased with increased ionic strength of the swelling medium. This behavior can be attributed to the charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. The swelling of superabsorbing hydrogels was measured in solutions with pH ranging from 1 to 13. In addition, the pH reversibility and on-off switching behavior, at pH levels of 3.0 and 8.0, give the synthesized hydrogels great potential as an excellent candidate for the controlled delivery of bioactive agents.

Preparation of fluorescent polymer particles by emulsion polymerization

AbstractCore-shell type fluorescent polymer particles were produced in multi-step emulsion polymerization. Cross-linking was introduced to the shell to suppress leakage of fluorescent dyes contained in the core particles. First, fluorescent polymer particles were synthesized by emulsion copolymerization of styrene (St) and butyl acrylate (BA) with an anionic surfactant (SE1025A) initiated by ammonium persulfate (APS) in the presence of pyrene. The concentrations of St, BA, SE1025A and APS were 550, 89, 8.2 and 5 mol/m3 water, respectively. Then the fluorescent particles were covered with cross-linked polymer by emulsion copolymerization of St, BA and divinylbenzene (DVB) with SE1025A emulsifier. In the polymerization, a mixture of St, BA, SE1025A and DVB was added dropwise to the reaction system. The average size of cross-linked fluorescent particles ranged from 50 to 70 nm. The fluorescence intensity of the particles prepared in a pyrene concentration range of 8 - 20 mol/m3 water increased linearly with pyrene concentration. Fluorescence intensities of the particles prepared with and without DVB were also measured. The cross-linked polymer formed by DVB addition drastically suppressed the intensity drop caused by dye leakage almost to one-third of the intensity drop measured for particles prepared without DVB addition.

Partially hydrolyzed crosslinked alginate-graft-polymethacrylamide as a novel biopolymer-based superabsorbent hydrogel having pH-responsive Properties

In this study, a series of highly swelling hydrogels based on sodium alginate (NaAlg) and polymethacrylamide (PMAM) was prepared through free radical polymerization. The graft copolymerization reaction was performed in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator andN,N′-methylenebisacrylamide (MBA) as a crosslinker. The crosslinked graft copolymer, alginate-graft-polymethacrylamide (Alg-g-PMAM), was then partially hydrolyzed by NaOH solution to yield a hydrogel, hydrolyzed alginate-graft-polymethacrylamide (H-Alg-g-PMAM). During alkaline hydrolysis, the carboxamide groups of Alg-g-PMAM were converted into hydrophilic carboxylate anions. Either the Alg-g-PMAM or the H-Alg-g-PMAM was characterized by FTIR spectroscopy. The effects of the grafting variables (i.e., concentration of MBA, MAM, and APS) and the alkaline hydrolysis conditions (i.e., NaOH concentration, hydrolysis time, and temperature) were optimized systematically to achieve a hydrogel having the maximum swelling capacity. Measurements of the absorbency in various aqueous salt solutions indicated that the swelling capacity decreased upon increasing the ionic strength of the swelling medium. This behavior could be attributed to a charge screening effect for monovalent cations, as well as ionic cross-linking for multivalent cations. Because of the high swelling capacity in salt solutions, however, the hydrogels might be considered as anti-salt superabsorbents. The swelling behavior of the superabsorbing hydrogels was also measured in solutions having values of pH ranging from 1 to 13. Furthermore, the pH reversibility and on/off switching behavior, measured at pH 2.0 and 8.0, suggested that the synthesized hydrogels were excellent candidates for the controlled delivery of bioactive agents. Finally, we performed preliminary investigations of the swelling kinetics of the synthesized hydrogels at various particle sizes.

Modified carrageenan. 5. Preparation, swelling behavior, salt‐ and pH‐sensitivity of partially hydrolyzed crosslinked carrageenan‐graft‐polymethacrylamide superabsorbent hydrogel

AbstractThe polysaccharide, kappa‐carrageenan (κC) was chemically modified to achieve a novel superabsorbent hydrogel via graft copolymerization of methacrylamide (MAM) onto the substrate followed by alkaline hydrolysis. Ammonium persulfate (APS) and N,N′‐methylene bisacrylamide (MBA) were used as a free‐radical initiator and a crosslinker, respectively. The saponification reaction was carried out using sodium hydroxide aqueous solution. Either κC‐g‐PMAM or hydrolyzed κC‐g‐PMAM (PMAM: polymethacrylamide) was characterized by FT‐IR spectroscopy. The effect of grafting variables (i.e. concentration of MBA, MAM, and APS) and alkaline hydrolysis conditions (i.e. NaOH concentration, hydrolysis time and temperature) were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The swelling capacity of these hydrogels was also measured in various salt solutions. Results indicated that the swelling ratios decreased with an increase in the ionic strength of the salt solutions. This behavior can be attributed to charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. Absorbency of superabsorbing hydrogels was examined in buffer solutions with pH range 1–13. Also, the pH reversibility and on–off switching behavior, at pH values 3.0 and 8.0, makes the synthesized hydrogels good candidates for controlled delivery of bioactive agents. Finally, swelling kinetics in distilled water and various salt solutions was preliminary investigated. Results showed that the swelling in water was faster than in saline solutions. Copyright © 2004 John Wiley & Sons, Ltd.

PREPARATION AND CHARACTERIZATION OF SAWDUST/N-METHYLOLACRYLAMIDE/METHACRYLIC ACID CATION EXCHANGE COMPOSITES

Highly concentrated mixtures of methacrylic acid (MA) and N-methylolacrylamide (NMA) were polymerized in presence of purified sawdust using ammonium persulfate/sodium thiosulfate redox system in order to prepare sawdust/NMA/MA cation exchange composites. Polymerization was carried out under different conditions including the concentration of ammonium persulfate and sodium thiosulfate, temperature, liquor-to-sawdust ratio (LR) as well as concentration of both NMA and MA. Reaction conditions were optimized to prepare three cation exchange composites having capacities of 805, 615, and 530 meq/100 g. Potentiometric titration indicated that these composites were weak base cation exchangers and their strength, pK a, decreased by decreasing the capacity. Characterization involved also the durability test, water solubility, and water swellability.

Synthesis of Polymerizable Anionic Surfactants and Their Emulsion Copolymerization with Styrene

Two polymerizable ionic surfactants sodium 4-(ω-acryloyloxyalkyl)oxy benzene sulfonate (SABS-n, n = 8 or 10) have been synthesized and polymerized. Their critical micelle concentrations (CMC) were determined to be 9.40 × 10-3 M and 2.02 × 10-3 M at 25 °C for SABS-8 and SABS-10, respectively. The rate of micellar polymerization of SABS-8 or SABS-10 was found to be proportional to half an order of the concentration of ammonium persulfate (APS) and first order of the surfactant concentration. Their activation energies of micellar polymerization were relatively low, that is, 58.2 kJ mol-1 for SABS-8 and 45.4 kJ mol-1 for SABS-10. The monomer reactivity ratios for emulsion copolymerization of SABS-8 (M1) and styrene (M2) were determined to be r1 = 0.47 and r2 = 3.91. These emulsion copolymerizations produced small latex particles ranging from 16 to 30 nm in diameter. XPS analysis shows that SABS-8 was significantly enriched on the surface of latex particles, for example, 63.4% surface coverage on latex particl...

Graft copolymerization of 2-(dimethylamino)ethyl methacrylate onto carboxymethylated cellulose

Amphoteric graft copolymers of carboxymethylated cellulose (CMC) with 2-(dimethylamino)ethyl methacrylate (DMAEM) were prepared in aqueous solutions using ammonium persulfate (APS) and N,N,N ′,N ′-tetramethylethylenediamine (TMEDA) as the initiation system. They were characterized by the grafting parameters, IR and solubility measurements. The effects of the reaction variables on the grafting percentage of the graft copolymer (%GP), grafting efficiency of the reaction (%GE) and grafting conversion of the monomer (%GC) were studied. It is observed that the %GP, %GE and %GC increase and then decrease with increasing concentrations of TMEDA and APS, pH of reaction medium and polymerization temperature. Increasing DMAEM amount is accompanied by an increase in the %GP but the opposite holds true for CMC. Under similar conditions, %GP, %GE and %GC increase upon increasing degree of substitution of carboxymethyl groups of CMC up to a value of 0.22, beyond which %GP and %GC did not cause a significant change while %GE decreases. Addition of an appropriate amount of salt to the synthesis system is favorable for the grafting. The overall activation energy for the grafting is calculated to be 10.3 kJ/mol.

Kinetics of chemical oxidative dispersion polymerization of 3,5-xylidine in aqueous medium using a PH stat method

Kinetics of chemical oxidative dispersion polymerization of 3,5-xylidine (Xy) in aqueous medium with ammonium persulfate (APS) as an oxidant was studied by monitoring the amount of proton released from Xy monomer, which was obtained from the amount of potassium hydroxide (KOH) solution added to keep constant pH values using a pH stat. The initial polymerization rate (R) [mol/L/min] of Xy was expressed as follows: R = 1.65 (1 − α) [Xy] [APS], where α is the degree of ionization of Xy, and [Xy] and [APS] are concentrations of Xy and APS, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4238–4246, 2000